1. Field of the Invention
The present invention relates to a developing apparatus used in image forming apparatus of electrophotographic or electrostatic recording type and adapted to develop an electrostatic latent image on an image bearing member.
2. Related Background Art
Nowadays, an image forming apparatuses of electrophotographic type have widely been used as copying machines, printers or the like, and, in such image forming apparatuses, an electrostatic latent image formed on an electrophotographic photosensitive member is developed with developing agent (referred to as "toner" hereinafter) as a toner image which is in turn transferred onto a recording medium. In a developing apparatus for effecting development with toner, as shown in FIG. 12, for example, a cylindrical developing sleeve (toner convey means) 52 having a magnet member 51 therein is rotatably attached to an opening portion of a toner container 50 containing two-component toner comprised of magnetic toner or magnetic carrier and non-magnetic toner, and the toner is transferred to an electrophotographic photosensitive member 53 by the developing sleeve.
In recent years, such a developing apparatus can detachably mounted to the image forming apparatus and such a developing method has been applied to an image forming apparatus using a process cartridge including an electrophotographic photosensitive member and a developing apparatus.
In the developing apparatus, elastic seal members 54 are attached to the developing sleeve 52 and both ends of the opening portion so that toner is prevented from leaking through the ends by the seal members 54. However, with this sealing arrangement, since the elastic seal members 54 are urged against the outer peripheral surface of the developing sleeve 52, rotational load of the developing sleeve 52 becomes great, and sealing ability may be reduced by degradation of the elastic seal members 54.
To avoid this, in case where the toner is magnetically absorbed, it is considered that magnetic sealing is achieved by a magnetic force generating means. For example, as shown in FIG. 13, at each longitudinal end of the developing sleeve 52, a magnetic seal member 55 having N and S poles arranged alternately in a rotational direction of the developing sleeve 52 is provided on a surface opposed to the developing sleeve with a predetermined gap g therebetween so that the toner is held magnetically. With this magnetic sealing arrangement, since the magnetic seal members 55 are not contacted with the developing sleeve 52, the rotational load of the developing sleeve 52 becomes small, and, since there is no degradation of the seal members due to wear, recycle of the magnetic seal members 55 is permitted.
In the above-mentioned magnetic sealing arrangement, when the gap g between the developing sleeve 52 and each magnetic seal member 55 is made smaller, the magnetic force of the magnetic seal member 55 can substantially be increased thereby to improve the sealing ability, and, thus, it is preferable. However, if the gap g is made extremely small, when the toner passed through the developing area is collected in the toner container again, scattering and leakage of toner are apt to occur.